Unusual rib structure?

[Delwin D Fandrich]

----- Original Message -----
From: "Ron Nossaman" <RNossaman@cox.net>
To: "Pianotech" <pianotech@ptg.org>
Sent: May 08, 2003 9:22 AM
Subject: Re: Unusual rib structure?


> As many concave crowned soundboards as I find with no measurable string
> bearing in the killer octaves of pianos with "rib crowned" boards, I
> suspect that these are indeed compression supported boards with crowned
> ribs. Doing load analyses on these ribs, with string scale and bearing
> schedules taken from the piano (allowing for what was probably in the
> killer octave before it went flat), and considering the feathering of
these
> ribs, I see no way those ribs are holding up even half of the string load
> placed on the soundboard assembly. They may be rib crowned, but they're
not
> rib supported.  And as long as the ribs are feathered that way, they
won't
> be.
>
> Ron N


Which is why we don't feather ribs that way. Basically, the rib is divided
into thirds. Feathering starts about one-third of the way in from each end
(depending on the location of the bridge) and is flat, not concave.

Del